Genes and Inheritance

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Genes and Inheritance

• We know from previous discussions that an egg
  contains half of the information needed to make a
  baby, and a sperm contains the other half.

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• This means that when the egg is fertilized by the
  sperm, it results in a cell that has the exact
  number of chromosomes required to make a new
  human being.

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• It also means that each baby gets half of its
  genetic information from its mother, and half
  from the father.

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• A trait is a particular feature that you can see
  in a person. Some examples of physical traits are
  hair color and eye color.
• Your physical traits are determined by your
  genetic information.

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• Each trait has two genes associated with it one
  from the mother and one from the father.

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• Most genes are one of two types. Dominant genes
  are the ones that take over.
• If there is a dominant gene present in a pair,
  then that is the trait you will see. It is like
  the boss.

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• Recessive genes are the ones that are easily
  hidden.
• They take a back seat to the dominant ones.
• The only time you will see a recessive trait is
  if there is no dominant one to take over.

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• When we write about traits, we pick a letter.
• Then we use the capital letter to represent a
  dominant gene, and a lower case letter to
  represent a recessive gene.

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• The genotype of a person is the combination of
  which two genes they have for a particular
  triait. For example, for eyes a person could be
  BB, Bb, or bb.

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• This would be called the persons genotype.
• If the two letters are the same case, we call the
  person homozygous for that trait.
• If the two letters are different, we call the
  person heterozygous for that trait.

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• The phenotype of a person is what you actually
  see because of their genes.
• So for eyes, the phenotype would be blue eyed or
  brown eyed.

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Note

• The genes that determine sex are a little
  different than normal. Females have two matching
  genes, usually called X. So every female is
  homozygous for the sex gene, genotype XX.
• Males have two different genes called X and Y, so
  they are heterozygous for the sex gene, genotype
  XY. This means each sperm can carry either X of a
  Y chromosome. In this way, the sex of the baby is
  determined by the male parent.